Conventional radiation detectors, which may e.g. be utilized in computed tomography applications, usually comprise a scintillator coupled to a photo diode to convert an X-ray flux into optical light and thereafter into an electrical current, i.e. a charge per unit time. The current from the photo diode is usually converted and digitized by a current-to-frequency converter and a digital counter.
In order the keep the electronics at an appropriate operation point for low X-ray flux, usually a bias current parallel to the current from the photo diode is supplied to the current-to-frequency converter, which bias current generates an offset of the current supplied to the current-to-frequency converter.
Such radiation detectors usually suffer from a number of noise sources, such as for example the 1/f noise of the bias current. At a low X-ray flux this noise may become even more pronounced and may set limits for ultralow dose imaging.
US 2012/0097856 A1 discloses an imaging detector with a photosensor array optically coupled to a scintillator array, wherein a current-to-frequency converter as described above is utilized.